Chemistry 1010 The Periodic Table: How the Elements are Organized
Review Name some elements that you remember from the previous lecture, and what you remember about them. gold and copper are the only metals that aren't gray Where do the names of the elements come from? from names of substances, what they were found in, mythology, scientists, places What are the symbols for the following elements? argon Ar nickel Ni arsenic As neptunium Np astatine At nitrogen N antimony Sb niobium Nb
What is the most common element in the universe? What is next? hydrogen, helium (99.75%) What are the two most common elements on the earth? oxygen, silicon (75%) What are the four most common elements in your body? oxygen, carbon, hydrogen, nitrogen (96%) What are the three categories of elements based on what they look like in their pure form?? metals (74) nonmetals (17) metalloids (6) unknown (21)
If a pure element can exist in two or more different forms, what are these forms called? allotropes How many elements can be found native (in their pure form in nature)? gold, silver, copper, platinum, iron, carbon, sulfur 7 How are the other elements found? in compounds and mixtures
Introduction Take a good look at the Periodic Table of Elements that you were given. What objective observations can you make about it?
What does each block of the Periodic Table contain? each block represents one element atomic number symbol name atomic mass
Why isn't the atomic mass a whole number? more than one isotope exists in nature 99.98% have 1 proton; mass = 1 0.015% have 1 proton, 1 neutron; mass = 2 1 in 1018 have 1 proton, 2 neutrons; mass = 3 mass of hydrogen found in nature: 1.007 What about atoms whose mass is a whole number in parenthesis? for most radioactive elements, the mass of the most stable isotope is shown
Today we will discuss the Periodic Table. 1. Why did chemists need a new way to organize the elements? 2. What does periodic mean? 3. How does the Periodic Table show repeating patterns? 4. How can the Periodic Table be used to predict the properties of elements?
1. Why did chemists need a new way to organize the elements? There are lots of ways that you could organize a list of elements. How is this list organized? alphabetically actinium aluminum americium antimony argon arsenic astatine barium berkelium beryllium bismuth bohrium boron bromine cadmium calcium californium carbon cerium cesium chlorine chromium cobalt copernicium copper curium darmstradtium dubnium dysprosium einsteinium erbium europium fermium fluorine francium gadolinium gallium germanium gold hafnium hassium helium holmium hydrogen indium iodine iridium iron krypton lanthanum lawrencium lead lithium lutetium magnesium manganese meitnerium mendelevium mercury molybdenum neodymium neon neptunium nickel niobium nitrogen nobelium osmium oxygen palladium phosphorus platinum plutonium polonium potassium praseodymium promethium protactinium radium radon rhenium rhodium roentgenium rubidium ruthenium rutherfordium samarium scandium seaborgium selenium silicon silver sodium strontium sulfur tantalum technetium tellurium terbium thallium thorium thulium tin titanium tungsten uranium vanadium xenon ytterbium yttrium zinc zirconium advantage: easy to find an element problem: doesn't tell us anything about properties
How was Dalton's 1805 list of elements organized? by mass advantage: you can see what elements are lighter and which are heavier problem: you can't predict any other properties How is the list that I gave you organized? by atomic number elements go up in mass and atomic number almost identically
As more and more elements were being discovered, chemists tried to find a way to organize them that would show how their properties were related. A chemist named Dmitri Mendeleev discovered the key. Mendeleev was a card player. He wrote the names, masses, and properties of the 63 known elements on playing cards and shuffled and dealt them again and again, looking for a good way to organize them. Eventually he realized that: when elements are listed in order of their mass, their properties are periodic
2. What does periodic mean? If something is periodic, then it: has properties with a repeating pattern Let's consider some examples of things you are familiar with: numbers, letters, days of the month, temperature, and wind speed. Numbers: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 etc Is there a pattern to how we write the numbers? yes 0 to 9 are different, but then it starts over at 10-19
How could you make a chart to represent this? If you go across the rows of this table: the first digit is the same the last digit is in order of size If you go down a column of this table: all of the numbers end in the same digit Are numbers periodic? yes pattern repeats itself exactly
Letters: ABCDEFGH I JK LMNOPQRSTUVWXYZ Are there any repeating patterns in the letters? not really We could make a chart by starting a new row every time there is a vowel. Across the rows: goes up one letter Down the columns: nothing in common Are the letters periodic? no
Days in a month: Sat, Dec 1 Mon, Dec 2 Tues, Dec 3 Wed, Dec 4 Thurs, Dec 5 Fri, Dec 6 Sat, Dec 6 Sun, Dec 7 Mon, Dec 8 Are there any repeating patterns? days of the week repeat How can we make a chart showing this? rows dates go across, then continue on the next row columns all the same day of the week Are days of the month periodic? yes!
Temperature: If you took the outside temperature every three hours for five days, what pattern would you see? it would get colder in the night, then warmer in the day We can show this by making a graph. the graph shows the repeating pattern Is temperature periodic? yes
Wind speed: If you took the wind speed every three hours for five days, what pattern would you see? there probably wouldn't be one Here's what the graph would look like: no repeating pattern Is wind speed periodic? no Graphs can show whether something is periodic or not. If something is periodic, a table will show a relationship both across rows and down columns.
Elements: Here are three graphs showing different properties of the elements. Is there a repeating pattern? yes size of atoms (atomic radius)
yes first ionization potential
yes electronegativity Since the elements are periodic, there must be a way to make a chart which will make use of these repeating patterns.
3. How does the Periodic Table show repeating patterns? To show how Mendeleev used the repeating patterns in the elements to create the Periodic table, we'll use a set of colored cards with numbers on them. numbers = mass of the element colors = properties of the element Step 1: Random order (this is like an alphabetic list of the elements) 15 1 10 4 11 17 5 20 8 12 21 9 6 18 16 22 14 3 19 7 13 2
Step 2: Arrange the cards in a long row in numerical order (this is like a list of the elements in order of mass) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 What patterns do you see here? blue always comes after orange green is always followed by yellow purple is always between a blue and a green yellow always has an orange after it and so on
Step 3: Turn the row into a table by starting over every time there is an orange card. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Step 4: Slide the cards over so that the columns match up. 1 2 3 5 6 9 10 14 19 4 7 8 11 12 13 15 16 17 18 20 21 22 rows: numbers go up by one (may jump across) columns: same color
How does the table you have made compare to the Periodic Table of Elements? rows: increase in both atomic number and mass columns: elements with similar properties
Draw arrows to show how the atomic number increases:
What's going on with the two rows at the bottom of the table? Here's what the Periodic Table should really look like: To make the table smaller, they took some elements out of the middle and made them into two separate rows.
If a new element with the atomic number 119 was created, where would it go? 119 It would start a new row beneath francium.
Rows are called periods. Periods are numbered from the top. 1 2 3 4 5 6 7 What period are the following elements in? beryllium (4) 2nd period tungsten (74) 6th period titanium (22) 4th period curium (96) 7th period
Columns are called families or groups. Some families have names. carbon family noble gases alkali metals halogens alkaline earth metals All other columns are named after the first element in the family.
Elements in the same family have similar properties. Halogens all occur in pure form as diatomic molecules which are highly reactive fluorine chlorine bromine iodine all form a highly acidic compound with one hydrogen atom and one halogen atom hydrogen hydrogen fluoride chloride hydrogen bromide hydrogen iodide
all form a 1:1 compound with sodium where the halogen has a -1 charge sodium fluoride sodium chloride sodium bromide sodium iodide all form a compound with one halogen atom, one carbon atom, and three hydrogen atoms fluoromethane bromomethane chloromethane iodomethane
noble gases all occur in pure form as colorless gases all are highly unreactive, forming few if any compounds with themselves or other elements all give off light in gas discharge lamps
alkali metals all are soft, highly reactive metals in pure form lithium sodium potassium rubidium cesium all easily lose one electron to form +1 ions all react with water to form hydrogen gas (which ignites!) lithium sodium potassium + + + water water water rubidium + water cesium + water
alkaline earth metals all are reactive silver colored, soft metals (but less reactive and harder than alkali metals) beryllium magnesium calcium stronium barium all are more dense than alkali metals and melt at very high temperatures stay solid in a fire Li 180oC Na 98oC K 63oC Rb 38oC Cs 28oC Fr 27oC Be 1278oC Mg 650oC Ca 839oC Sr 764oC Ba 725oC Ra 700oC all react with water, but not as vigorously as alkali metals all form compounds with chlorine with a 1:2 ratio LiCl NaCl KCl RbCl CsCl FrCl BeCl2 MgCl2 CaCl2 SrCl2 BaCl2 RaCl2
4. How can the Periodic Table of Elements be used to predict the properties of elements? When Mendeleev first published his Periodic Table in 1869, there were only 63 known elements, which is only about 2/3 of the naturally occurring elements. 1 2 3 6 9 10 14 20 mass increase down similar elements are across 7 11 16 17 21 22 So his cards actually looked more like this!
Mendeleev used the patterns that he had found to do something rather astonishing. When there was a space in the pattern with no element to fill it, he left a space open and predicted that a new element would be found to fill it. Within a few years, three of these elements were found in nature. 1875? = 68 gallium (actual mass 69.72) 1879? = 45 scandium (actual mass 44.96) 1886? = 70 germanium (actual mass 72.61) 1925? = 180 rhenium (actual mass 186.2)
Can you predict the cards that are missing in this table? 1 2 3 5 6 9 10 14 19 4 7 8 11 12 13 15 16 17 18 20 21 22 23 What else is missing?
Here is what our current table looks like with only the elements Mendeleev knew: What's missing? Sc, Ga, Ge, Re, hafnium (1923) noble gases (1894-1898) radioactive elements (1898-1900) rare earth elements (1878-1901) artificial elements (1939-present)
Let's look at some of the patterns the Periodic Table reveals. Where are the naturally occurring and artificial elements? naturally occurring artificial 43 104 118 61 93 artificial elements = 43, 61, 93-118 103
Where are the metals, nonmetals, and metalloids? metals metalloids nonmetals At Fr Sg Uuh Md What would you guess about the appearance of the following elements? francium metal mendelevium metal seaborgium metal ununhexium metal astatine nonmetal or metalloid
Here is a visually beautiful Periodic Table created by Theo Gray. You can order a 20 x 40 poster for $15 at his website.
How are the metals divided up? main group metals (nonmetals) transition metals inner transition metals
Where are the solids, liquids, and gases? solids liquids gases Can you predict the physical state of the unknown elements? all solids except Uuo, which is probably a gas